Distributional notes
Originally known only from Japan, this species was first found in British Columbia in 1944 and in Oregon in 1947. It first appeared in northern California in 1963 (Crescent City), southern California in 1970 (Santa Catalina Island), and in San Francisco Bay in 1973 (Berkeley). Also in 1973, it was found for the first time in the north Atlantic at Bembridge, Isle of Wight, on the south coast of England (Farnham, Fletcher & Irvine, 1973), as predicted by Dreuhl (1972). The species is now widely distributed from Norway to Spain. It now occurs throughout the north Pacific, north Atlantic and Mediterranean showing an extraordinary ability to tolerate a wide range of conditions and is regarded as highly invasive (Norton, 1976). Silva (1979: 338) observes preceptively: "It is a weed in the sociological sense of a plant growing outside its original range and in such a manner as to be unwanted." A single plant was found in O'ahu, Hawai'i attached to the hull of a barge that had been towed from San Diego in California, but the species does not seem to have established itself in Hawai'i (Abbott & Huisman, 2004). Critchley et al. (1990) gives a comprehensive account of the spread of this entity up to 1990. See also Verlaque et al. (2015: 95) who regard this species as a "pest and fouling organism" in the Mediterranean, where it first appeared in the Etang de Thau, France, in 1980.